1. Field of the Invention
The present invention relates to a fluid compressor suitable, for example, for compressing a refrigerant gas in the refrigeration cycle.
2. Description of the Prior Art
As compressors generally known so far, there can be mentioned reciprocal or rotary type compressors. Moreover, a helical-blade type fluid compressor is also well known. The fluid compressor of this type, as described in Japanese Patent Application No. 62-191564 for example, is so constructed that a refrigerant is applied into an operation chamber on the inlet side of a cylinder, then carried in the cylinder toward another operation chamber on the outlet side of the cylinder while being successively compressed, and is thereafter discharged from the cylinder.
For example, as shown in FIG. 1, the helical blade type compressor includes driving means 105 comprising a stator 101 fixed to an outer frame of the compressor and a rotor 103 rotatable in the stator 101, a cylinder 107 integrally joined to the rotor 103, and a rotary rod 111 which is orbited by means of an Oldham ring 109 rotatable about an eccentric axis spaced by a distance e apart from the central axis of the cylinder 107. Namely, all of these roter 103, cylinder 107 and rotary rod 111 are rotated to the stator 101, so that the rotary rod 111 is helically orbited to the cylinder 107. Moreover, a spiral groove 113 is formed in the outer surface of the rotary rod 111 over almost all of the lateral length thereof, and a blade 115 is detachably fitted in the groove 113. Besides, the outer surface of the blade 115 is partly in contact with the inner surface of the cylinder 107 so that the blade 115 rotates together with the cylinder 107.
Because the rotary rod 111 is helically orbited about the eccentric axis shifted by a distance e from the central axis of cylinder 107, the rotation speed of the cylinder 107 differs from that of the rotary rod 111, and the difference is changed at a cycle of one rotation of the rod 111. Moreover, since the blade 115 flexibly moves along the groove 113 during the rotation, the space defined between the rotary rod 111 and the cylinder 107 are divided by the blade 115 so as to form a plurality of operation chambers 117. Therefore, each capacity of the operation chambers is determined by the pitch of the spiral groove 113 in which is fitted the blade 115 upon a determination of an inside diameter of the cylinder and an outside diameter of the roter.
Incidentally, the pitch of the groove 113 is gradually reduced from one end to the other of the rotary rod 111. Namely, according to the construction shown in FIG. 1, since the capacity of each operation chamber 117 formed by the blade 115 is gradually reduced toward the discharging side of the cylinder 111, corresponding to an outlet pipe 121, from the inlet side thereof, corresponding to a suction pipe 119, a refrigerant supplied from the inlet side is successively carried toward the discharging side through the plurality of operation chambers 117 while being gradually compressed.
Thus, according to the above-mentioned helical blade type fluid compressor, the refrigerant compression efficiency is decided by the ratio between capacities of the operation chamber nearest to the inlet and the chamber nearest to the outlet. Therefore, one means for enhancing the efficiency of the compressor is to enlarge the capacity of the operation chamber, which is nearest to the inlet. That is, the first operation chamber 117. Moreover, to enlarge the capacity of the first chamber 117, as shown in FIG. 2, it is necessary to either enlarge the first pitch P of the spiral groove 113 on the inlet side (shown on the right side in the same drawing) to make larger the diameter of the cylinder 107, or to make smaller the diameter of the rotary rod 111.
However, if the first pitch P of the spiral groove 113 is enlarged, the torsion stress imposed on the blade 115, around the area corresponding to the pitch P, will be so large that the blade 115 is likely to be fatigued. As the result, it is very difficult to guarantee the durability of the blade 115 and to prevent its breakage.
On the other hand, if the diameter of the cylinder 107 is enlarged, the inner diameter of the rotor 103 must be increased, such that efficiency of the motor is degraded, and the weight of the cylinder 107 and rotary rod 111 is increased. In particular, in this case, since the load of the rotor 103 to be imposed on a bearing section 123 is increased, the bearing section 123 is likely to be damaged, such that it is very difficult to stably support rotor 103 at its right and left side with a high degree of accuracy during assembly of the compressor. Moreover, since the stator 101 and rotor 103 must be enlarged with the enlargement the cylinder 107, it is necessary to increase the dimensions of the entire system. Additionally, an increase of the relative speed between the bearing section 123 and the cylinder 107 in proportion to the enlargement in diameter of the cylinder results in an increase of the driving loss of the compressor. When the diameter of the piston become smaller, since the eccentric value becomes large, the amount of the blade which must be inserted into the piston is increased. Therefore, it is difficult to make the rotor smaller.